Figure 2.

Trastuzumab charge heterogeneity is highly influenced by asparagine deamidation and aspartic acid isomerization. (a) The chromatogram resulting from our CVMS method is highly similar to the trastuzumab charge variant profile previously reported by Harris et al. showing amino acid site-specific charge variant peak assignments based on fractionation and peptide mapping data.²³ Delta masses are plotted for the seven major peaks. (b) Pathway for asparagine deamidation and aspartic acid isomerization. Deamidation of asparagine to aspartic acid results in a mass difference of +0.98 Da and changes the local pKa from basic (8.8) to acidic (3.9) and results in earlier elution by cation exchange separation. Isomerization of aspartic acid results in zero mass change and does not directly result in any predictable change to pI.